1. Field of the Invention
This invention is related to the measurement of ultrasonic velocities in materials. In one aspect this invention is directed to triaxial test apparatuses and methods employing ultrasonic transducers to measure ultrasonic velocities of low permeability rocks during a triaxial test.
2. Description of Related Art
A conventional triaxial test apparatus for rock testing is shown in FIG. 1. With such an apparatus, a test is performed inside an enclosed housing or hydraulic cell. A confining fluid is pumped into the test cell to provide a confining pressure on a rock sample specimen. The sample is placed on a bottom end cap for support. Hydraulic pressure is applied around the sample during the test to generate an isostatic confining stress. Then an axial load is applied (e.g. by a load piston) to a top end cap to generate a deviatoric (shear) stress.
Ultrasonic transducers have been used within end caps near opposite sides of a rock sample during tests. Ultrasonic waves from such transducers must pass through the end cap material, a material (usually metal) which alters the ultrasonic waves and affects them differently from the manner in which they are propagated through the material to be tested. This results in errors in measurement of velocity.
Applicants are unaware of any prior art disclosing test apparatuses and methods for materials which employ ultrasonic transducers adjacent the material to be tested to measure ultrasonic velocity in the material during a test.
There has long been a need for test apparatuses and methods for accurately measuring ultrasonic velocities of materials in which ultrasonic waves are not attenuated when going through material other than the material to be tested. There has long been a need for triaxial test apparatuses and methods which effectively and accurately measure ultrasonic velocities while simultaneously measuring pore pressure of a sample.